Developers commonly break user stories into tasks to facilitate distributing the implementation work across the team, and allow tracking of progress at a finer level of granularity. It seems perfectly logical.
I was recently working with a team who's stories seemed simple on the surface, but once the iteration started, new tasks kept surfacing. This resulted in many tasks getting completed in an iteration, but no stories.
Ron Jeffries has seen this situation as well. His suggestion is:
"Do stories as a unit, not broken into tasks." He wrote about it in a post called
Tasks are teh suck. I wrote about it in Burn Stories Not Tasks on InfoQ.
I helped the team I was working with to create smaller stories. They no longer felt the need to create and track tasks. More stories got done, resulting in happier customers and a happier more productive team.
Cheers,